ww: lib tests run via -T test mode; bare mains retired (closes @test conversion)

'ww test' gains the istest build path (-T injection in build_one/
buildone) and do_test/dotest accept -I, mirroring do_run - both twins.
The 35 converted lib tests drop their interim bare mains (-T
synthesizes the entry from @test fns and rejects a user main); their
35 C run-drivers flip 'ww run' -> 'ww test'; 989_lib_byteid compiles
lib tests under -T (8 user-main probe fixtures stay non-T, gated on
the fixture field). Abort-on-first-failure stands until the deferred
record-and-continue harness lands with the multi-package arc.

lib/strconv/test/stoftest.ww

@@ -225,11 +225,3 @@ fn nan32(s: str) bool = {
 	assert(!(!ovf32("1.0p+128", base.HEX)));
 	assert(!(!chk32("1.0p-151", base.HEX, 0.0f32)));
 };
-
-export fn main() i32 = {
-	stof64_dec();
-	stof32_dec();
-	stof64_hex();
-	stof32_hex();
-	return 0;
-};